High-Q/V LiNbO3 photonic crystal nanobeam cavity

Abstract

I investigated lithium niobate (LN) photonic crystal nanobeam cavities as a high-quality factor (Q) to mode volume (V) ratio optical platform. The LN photonic crystal nanobeam cavity was designed to demonstrate a transverse-electric fundamental mode with a Q/V ratio of 1.6 × 10^7 (λ/n)^−3, using numerical simulations by the finite element method and the finite-time time-domain method. The LN photonic crystal nanobeam cavity was created as a free-standing structure using focused ion beam (FIB) milling and a wet-etching process, resulting in a high sidewall angle of 85 °. Employing a U-shaped tapered optical fiber, I characterized the LN photonic crystal nanobeam cavity. The measured intrinsic Q factor and expected Q/V ratio were 6.7 × 10^3 and 7.9 × 10^3 (λ/n)^−3, respectively. The experimentally obtained Q factor was lower than the theoretical value due to downward bending and the insufficient buffer air layer of the free-standing LN photonic crystal cavity. Utilizing a thicker LN film and buffer layer would enhance the Q/V ratio of the photonic crystal cavity, thereby demonstrating potential for quantum optical and optomechanical applications in the future.